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Research Articles

ScienceAsia 33 (2007): 069-077 |doi: 10.2306/scienceasia1513-1874.2007.33.069

Growth, Survival and Field Performance of Bradyrhizobial Liquid Inoculant Formulations with Polymeric Additives

Panlada Tittabutra, Waraporn Payakaponga, Neung Teaumroonga, Paul W. Singletonb, and Nantakorn Boonkerda*

ABSTRACT: Liquid inoculant has become a preferred method for inoculating legumes with bradyrhizobia. Finely ground peat has been the standard of quality for inoculants for many years. Suitable peat for an inoculant carrier is difficult to find and limited in supply in many locations. We evaluated six different polymeric additives (polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG), polyvinyl alcohol (PVA), gum arabic, cassava starch, and sodium alginate) for their ability to support growth and promote survival of several strains of bradyrhizobia and rhizobia during storage. Some concentrations of various additives to yeast extract mannitol (YEM) media promoted higher cell density compared to cells cultured in YEM media alone. There was a large interaction between strains of rhizobia and the additives in relation to cell survival. Shelflife of liquid inoculant formulations depended on the strain of rhizobia and additives, when stored at room temperature. Liquid inoculants formulated with sodium alginate promoted long-term survival of all rhizobial strains, but its effect on cell survival was not as great as peat. Peat also provided the greatest protection to cells of bradyrhizobia after application to the seed surface followed by incubation at 40°C. Survival of bradyrhizobia was maintained at 105 cells/seed after 48 hours of incubation. Liquid inoculant formulated with gum arabic, sodium alginate, PVP, or cassava starch supported survival at only 104-105 cells/seed, while PEG and PVA additives performed poorly and cell numbers fell to 103 cells/seed at 48 hours after inoculation. One-week old liquid inoculants with bradyrhizobia were tested for their ability to nodulate and fix nitrogen under field conditions. We found that liquid inoculant performance was as good as that of peat based inoculant.

KEYWORDS: additive, bradyrhizobia, liquid inoculant, polymeric substance, survival.

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a School of Biotechnology, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand.
b Department of Tropical Plant and Soil Sciences, University of Hawaii at Manoa, Honolulu, HI 96822, USA.

* Corresponding author, E-mail: nantakon@sut.ac.th

Received 13 Sep 2005, Accepted 5 Jul 2006